A thermochromic material consisting of electron-donating and coloring organic compounds, electron-accepting compounds and desensitizers and a thermochromic material formed by encapsulating such components are known (see, Japanese Examined Patent Publication No. 14270/1989). Leuco dye employed in said thermochromic material is very inferior in resistance to light so that ultraviolet absorber is usually blended with the thermochromic material. When an ultraviolet-curable thermochromic ink composition is prepared by blending said thermochromic material with a photopolymerizable resin composition, a problem of undercure of an ink applied to printed face arises.
Said ultraviolet absorber prevents deterioration of leuco dye caused by light, only when the ultraviolet absorber has an absorption wave range of 220-380 nm. Resistance to light of thermochromic material is not improved by using an ultraviolet absorber having a longer absorption wave range (e.g. 380-450 nm).
It is a primary object of the present invention to provide a thermochromic ink composition comprising ultraviolet absorber suitable for leuco dye, wherein the composition is free of undercure of the ink and excellent in resistance to light and curing characteristics.